1. Field of the Invention
Embodiments of the present invention relate to systems and methods for reducing vapor emission from deck leg apertures of floating roof storage vessels.
More particularly, embodiments of the present invention relate to systems and methods for reducing vapor emission from deck leg apertures of floating roof storage vessels, where the vessels include a deck leg aperture vapor reduction system.
2. Description of the Related Art
A large number of petroleum above ground storage tanks (AST's) were built prior to 1980 and prior to the EPA more stringent regulations regarding hydrocarbon vapor emission control. The latest emission control standards require the use of the best available control technology (BACT) to minimize the vapor emissions. The new standards have required companies with older storage tanks to find practical ways to retrofit existing tanks to achieve compliance.
The purpose of a leg sleeve on an internal floating roof (IFR) storage tanks is to allow for the insertion of pipe legs in order to support the floating roof during maintenance activities. Normal out of service maintenance of the tank bottom is performed in the high leg position to allow safe entry under the roof. When the tank is returned to service the pipe legs are removed from the sleeves and placed on the floating roof until the next out of service maintenance is required. The remaining leg sleeve penetration in the roof is where vapor emissions can occur. In an effort to minimize the cost of taking tanks out of service and modifying each leg sleeve, most AST owners have adopted the simple approach of installing an impermeable bag or leg sock over the leg sleeve to minimize vapor emissions.
The existing technology is able to achieve compliance; however, the devices are not as effective as the vapor plug design and are difficult to maintain. In some cases these bags or socks do not seal well around the leg sleeve and rip or tear from the installation process and material fatigue. These rips or tears in the bags or socks can be found during required inspections and can result in owners receiving Notice of Violation (NOV) from the governing Air District. These fines can carry stiff penalties in some cases.
New technology is typically presented to the local Air Pollution Control District Agency, and after documented testing is confirmed, the Agency may consider it to be BACT and even establish a lower emission factor for the technology compared to other devices. A lower emission factor would create potential savings when purchasing emission credits for future processing and storage of petroleum products.